Spontaneously developable photosoluble silver halide dispersions and elements



United States Patent US. CI. 96-94 13 Claims ABSTRACT OF THE DISCLOSURE Photosoluble silver halide dispersion layers comprising, before imagewise exposure to light, silver halide crystals that are 1) spontaneously developable and (2) have associated therewith, in substantially greater than fog-inhibiting amounts, a silver salt of a 2-mercapto-4- oxazole, thiazole or iminazole having a 4 to 8-membered hydrocarbon nucleus linked to the 4 and/or S-carbon atom of the azole nucleus, the silver salt being of lower solubility in water than silver chloride and the associated silver halide crystals being less soluble in sodium thiosulfate than untreated crystals, and processes of exposing and processing same. The new photosoluble elements form visible silver halide images which may be intensified by reduction to silver in a conventional nonfogging developer without immediate light fogging prior to intensification.

This application is a continuation-in-part of my copending application Ser. No. 377,122 filed June 22, 1964 and entitled Emulsion Layer and Elements, now abandoned.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to photosoluble (or photosolubilizable) silver halide layers and elements containing the same wherein the layers are spontaneously developable being made by prefogging the treated silver halide crystals with radiation and/or by means of chemicals.

Description of the prior art There are a number of recently granted US. patents on photosoluble layers and elements and processes of image formation using them. Among these patents are 3,155,506-7, 3,155,514-9 (all patented Nov. 3, 1964), the two believed to be most pertinent to the present invention being 3,155,507 and 3,155,519.

Blake 3,155,507 relates to a process which comprises in the order stated, the steps of (a) exposing, imagewise, to actinic radiation a photosoluble silver halide layer containing silver halide crystals made relatively less soluble in a silver halide solvent (e.g., sodium thiosulfate) by treatment with an organic compound capable of forming a silver salt and whose silver salt is less soluble in water than silver chloride, and (b) prior to any reducing step, treating the element with an aqueous solution of a silver halide solvent, thereby efiecting solubilization of the silver halide in more exposed areas at a rate substantially greater than in less exposed areas until a positive image comprised of silver halide is produced. Subsequently the silver halide image can be intensified, e.g., by reduction to a silver image.

Blake 3,155,519 relates to photographic silver halide layers of the type described in the previous paragraph but one where the silver salt is a silver mercaptide of a 2- mercaptothiazole having a hydrocarbon nucleus of 4-12 3,490,909 Patented Jan. 20, 1970 carbon atoms, preferably phenyl. Blake 3,155,519 claims photographic elements having layers of silver halide crystals previously made to have a lowered rate of solution in a silver halide solvent by treatment with an organic compound capable of forming a silver salt of lower solubility in water than silver chloride. Such elements are capable of yielding positive photographic images of silver halide by exposing them, imagewise, to actinic radiation and then treating in a solution of a silver halide solvent to remove silver halide in the exposed areas. This positive silver halide image can subsequently be intensified by various means, e.g., by reducing the silver halide image to a metallic silver image. The non-optically sensitized elements disclosed above are sensitive only to the shorter end of the visible spectrum, i.e., they cannot be exposed SUMMARY OF THE INVENTION The photosoluble silver halide layers and elements of this invention comprise photosoluble silver halide crystals that are spontaneously developable and have associated therewith in substantially greater than fog-inhibiting amounts a silver salt of a 2-mercapto-4-oxazole, thiazole or iminazole having a 4 to S-membered hydrocarbon nucleus linked to a 4 and/or S-carbon atom of the azole nucleus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The photographic layers and elements, e.g., films, plates and papers of this invention comprise, before exposure to actinic light, silver halide crystals that are (1) spontaneously developable, and (2) have associated therewith in substantially greater than fog inhibiting amounts a silver salt of an azole compound of the formula II II Rs-C C-SH where X is a member selected from the group consisting of S, O and NH, R is a hydrocarbon nucleus of 5-8 carbon atoms, e.g., amyl, cyclohexyl, phenyl, and p-methoxyphenyl, and R is a member selected from the group consisting of H and a hydrocarbon nucleus of 5-8 carbon atoms, i.e., the same nuclei as for R These silver salts are of lower solubility in water than silver chloride, the silver halide crystals so associated with the silver salt being less soluble in 10% aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH and the associated organic compound being present in such an amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin emulsion containing 10 g. of gelatin per mole Ag and .57 mg. of Ag per ml., and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of

sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous and essentially equal agitation of both dispersions for 30 seconds at 25 C. In the preferred layers and elements, any heavy metal salts present are noble metal salts.

The spontaneously developable silver halide crystals van be readily made by prefogging them with radiation and/ or by chemicals. In Example V, quantitative tests are disclosed in Sequence c which involve processing steps labeled Fix and Wash followed by intensification by treatment for 3 minutes at 68 F. with conventional agitation in a specified photographic developer solution labeled Developer A, followed in turn by a Final Fix. Silver halide crystals suitable in the present invention should be spontaneously developable (i.e., developable without further treatment by radiation or by chemicals) to the extent that over 25% by weight of the silver of said crystals remains as reduced (metallic) silver after being processed according to Sequence c.

In a practical embodiment of the invention, a gelatinosilver halide photographic emulsion is coated on a suitable support, and the coated element is bathed in a solution of a compound of Formula I which forms a silver salt in intimate association with the silver halide crystals of the photographic emulsion. In a more preferred manner, elements can be prepared by adding the organic compound to the photographic emulsion prior to coating, as also disclosed in Blake U.S. Patent 3,155,519. In either event, the coated element comprises silver halide crystals in intimate association with the said silver salt of the organic compound. The element is photographically fogged either by uniform exposure to actinic radiation or preferably by uniform chemical fogging. Either of these means of fogging the photographic element may occur during the preparation of the element, either before or after (but preferably before) the introduction of the organic compound which forms the silver salt in intimate association with the silver halide crystals. The fogged element thus prepared is capable of forming a positive, photo graphic image by imagewise exposure to actinic radiation followed by treatment with a silver halide solvent which removes silver halide more rapidly from the exposed than from the unexposed areas. The sensitivity of the element of this invention has been extended by the fogging action so that a positive image can be produced by exposure to long wave length visible light.

The positive silver halide image obtained after treatment with a silver halide solvent may, with or without a water-washing step, be dried and used without further treatment, e.g., for viewing by projection. It is frequently desirable, however, to intensify the silver halide image, e.g., by reducing it to a metallic silver image, by toning it with sodium sulfide, sodium selenide, etc. or by converting it to a dye image, e.g., by reacting it with a primary aromatic amine color developing agent in the presence of a color coupling compound either in the developing bath or previously present in the emulsion. Reduction to a metallic silver image is a particularly preferred process for intensification and in such a process the elements of this invention are especially advantageous. With elements like those disclosed in Blake, U.S. Patent 3,155,519, reduction of the silver image can be effected with a con ventional photographic developing agent, e.g., hydroquinone or N-methyl-p-aminophenol. Before reduction, however, it is customary to fog the emulsion by an overall flash exposure to White light. The elements of the present invention have the advantage that they do not require a flash exposure step. This elimination of such a step is quite significant and simplifies processing. Moreover, flashing is impractical and undesirable in darkrooms where multiple processing operations may be carried on simultaneously.

Suitable organic compounds which may be used to form silver salts in intimate association with the silver halide cry t ls i clude those azole co pounds coming within the scope of the above-designated Formula I. The utility or any such azole compound can be readily determined by relatively simple tests. Essentially, the utility is determined by Test A and Test B. In Test A, the candidate azole compound must render a dispersion of silver halide crystals insoluble in a silver halide solvent, e.g., an aqueous solution of sodium thiosulfate, at some pH between 1 and 13. If the candidate compound meets the insolubility requirements of Test A, it must also meet the requirements of Test B by forming with said dispersion of silver halide crystals a reaction product which, upon treatment with an aqueous solution of sodium hypochlorite, becomes soluble when subsequently treated with aqueous sodium thiosulfate. The following practical tests are provided in further exemplification of the invention and include specific concentrations of solutions, times, etc., so that suitable azole compounds may be readily and positively identified.

Test A A solution nearly saturated at 25 C. with a candidate azole compound is prepared using ethanol, acetone, dimethylformamide, water or other suitable solvents. Depending on the solubility, a solution concentration from 0.01 to 10 percent by weight is obtained. Twenty-five ml. of a gelatino-silver chlorobromide dispersion containing 25 mg. of silver halide (calculated as silver bromide), prepared as described below, is treated with small increments (i.e., about 0.1 to 0.2 ml. at a time) of the said candidate solution under safelight conditions (Wratten 1A filter or equivalent) until the silver halide dispersion either is rendered insoluble in 10% aqueous sodium thiosulfate or the candidate is found not to cause insolubilization. Generally insolubilization will occur upon the addition of 0.05 g. or less of said candidate compound, calculated as the pure compound. Compounds which must be used in substantially greater quantities than this, e.g., 1-2 g. to effect insolubilization are considered less preferred compounds. The silver halide dispersion insolubility is determined by taking a 0.5-ml. portion of the silver halide dispersion (after each incremental addition of the candidate azole compound), adding about 0.1 to 0.2 ml. of 10% aqueous sodium thiosulfate solution and observing the turbidity after 30 seconds.

As a control, there is used 25 ml. of Water to which small increments of the candidate solution are added. Half-milliliter portions of the control are treated in the same manner with the sodium thiosulfate solution. The presence of visual turbidity relative to the control solution is sufficient to satisfy the definition of insolubility in this test.

This test may be repeated for various pH increments from 1 to 13. Although there is some optimum pH value at which the test is most sensitive, this is not a sharp maximum which must be precisely attained. Rather, it has been found that there is a fairly broad range of pH values (e.g., 2.0 to 3.0 pH units) over which the test has a satisfactory sensitivity. In practice, the silver halide dispersion might be tested without adjustment (e.g., at pH 5.0 to 7.0) and if insolubilization occurs here, Test A is completed. If there is no insolubilization, the test is repeated at a higher pH (e.g., from pH 10-13). If there is still no insolubilization, the test is conducted with emulsion adjusted to a lower pH (e.g., about pH 1-3). Thus three different pH values represents a practical maximum number which must be investigated to determine whether or not insolubilization will occur.

Test B The azole compound-capable of insolubilizing a silver halide dispersion according to Test A is now ready for the next test, which again will be conducted under safe light conditions. To the above silver halide dispersion, there is added the minimum amount of a solution of the candidate azole compound found necessary for insolu-. bilization. Half-milliliter samples 613 the disp taining 0.5 mg. AgBr or 0.29 mg. Ag) are placed in two test tubes. To one sample is added 0.5 ml. of water; to the other is added 0.5 ml. of a 5% by weight aqueous solution of sodium hypochlorite (containing 25 mg. sodium hypochlorite). Next, there is added to both samples, 1.0 ml. of an aqueous by weight solution of sodium thiosulfate (containing 100 mg. sodium thiosulfate). If, after standing for up to thirty seconds, the sample treated with sodium hypochlorite clarifies (or becomes less turbid) relative to the control sample, the candidate azole compound meets the requirements of Test B and it is satisfactory for use as disclosed in this invention.

The silver halide dispersion discloses in Tests A and B above was a lithographic emulsion having a silver halide composition of 30 mole percent AgBr and 70 mole percent AgCl. The emulsion had grams of gelatin present per mole of silver halide for the steps of precipitation and ripening and was freed of unwanted, soluble, by-product salts by a coagulation and wash procedure as taught in US. Patent 2,489,341, wherein the silver halide and most of the gelatin were coagulated by an anionic wetting agent, sodium lauryl sulfate, using an acid coagulation environment. After washing, the emulsion coagulate was redispersed in water and without the use of additional bulking gelatin, maintaining a pH of 60:0.1 while stirring 10 min. at 110 F, Usually about 10 g. of gelatin is lost during washing, and the resulting emulsion contains about 10 g. of gelatin per mole of silver halide.

The amount of the silver azole salt present in the photographic silver halide layer should be suflicient to protect the silver halide crystals so that the unexposed crystals cannot be fixed by conventional fixing conditions, i.e., at normal times, temperatures and concentrations of silver halide solvents.

The gelatin/ silver halide ratio is quite flexible and may vary from 3:1 to 1:20 depending on the particular azole compound and intended use for the emulsion layer. The imagewise solution of the exposed silver halide/zole compound stratum may be eifected by the silver halide solvents commonly used as photographic fixing agents, e.g., sodium thiosulfate, alkali metal thiocyanate (e.g., sodium, potassium), concentrated solutions of potassium bromide, etc.

In intensifying the resulting silver salt image, reduction of the treated, residual silver halide may be accomplished by use of any chemical reducing agent capable of reducing silver ion to silver metal, e.g., hydroquinone, metol, sodium hydrosulfite and stannous chloride. The function of the reducing agent may be enhanced by modifying the surface properties of the treated, residual silver halide crystals by means of alcohol, thiourea, potassium iodide, etc.

The photographic compositions of this invention are pre-fogged, i.e., fogged prior to the imagewise exposure, in any convenient manner. The fogging may be carried out at any stage of manufacture. Chemical fogging can be achieved during the manufacture of the emulsion by admixing such chemicals as formaldehyde, formaldehydeyielding compounds, stannous salts such as stannous chloride, etc.

Fogging by exposure to radiation may be accomplished with any radiation which is actinic for the particular photographic emulsion, e.g., short wave length visible light such as blue or violet, ultraviolet radiation, X- radiation, gamma radiation, etc. The time and exposure intensity are not particularly critical since the treatment is effective over a wide exposure latitude. The chemicalfogging or light-fogging treatments must cause the spontaneous reduction of at least of the silver halide to silver when non-image exposed dry coatings of the silver halide are processed according to Sequence 0 of Example V.

In place of part of the gelatin, other natural or synthetic water-permeable organic colloid binding agents can be used and in some cases such binders can be used alone. Such agents include water-permeable or watersoluble polyvinyl alcohol and its derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers and acetals containing a large number of intralinear groups, hydrolyzed inter-polymers of vinyl acetate and unsaturated addition polymerizable compounds such as maleic anhydride, acrylic and methacrylic acid esters and styrene. Suitable compounds of the last-mentioned type were disclosed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinyl butyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal. Other useful colloid binding agents include the poly-N-vinyllactams of Bolton U.S. Patent 2,495,918, various polysaccharides, e.g., dextran, dextrin, etc., the hydrophilic copolymers in Shacklett US. Patent 2,833,650, hydrophilic cellulose ethers and esters, and polymers of acrylic and methacrylic esters and amides. Also, it has been found practical to apply silver halide layers on a base material in the essential absence of a binder, e.g., by chemical or vacuum deposition.

The emulsion may optionally contain any of the usual adjuvants customarily employed in silver halide systems as long as they do not interfere with the insolubilizing action of the essential ingredient (the silver salt of the azole compound) of the invention.

The emulsions can be coated on any suitable support, e.g., cellulose esters, cellulose mixed esters; superpolymers, e.g., poly(vinyl chloride co vinyl acetate), polyvinyl acetals, butyrals; polystyrene; polyamides, e.g., polyhexamethylene adipamide, polyesters, e.g., polycarbonates, polyethylene terphthalate, polyethylene terephthalate/isophthalate, esters formed by condensing terephthalic acid and its derivatives, e.g., dimethyl terephthalate wtih propylene glycol, diethylene glycol, tetramethylene glycol, cyclohexane-1,4-dimethanol (hexahydro-p-xylene dialcohol); paper, metal, glass, etc.

The desirable concentration of the azole compound which forms the required silver salt depends on many factors such as the solubility of the azole compound, the nature of its reaction with silver halide, the size and nature of the silver halide crystals, the presence of other materials which may react with or be absorbed to the surface of the silver halide, etc. Calculations given in Blake U.S. Patent 3,155,519 show that a useful concentration of the azole compound is approximately that which can be theoretically determined as required to cover the silver halide surface with a so-called monomolecular layer. As shown in the examples below, elements suitable according to this invention can be prepared by bathing a photographic film in a solution of an appropriate azole compound. In this embodiment, the silver halide crystals near the surface of the coated emulsion stratum are in contact with a higher concentration of the azole compound. Crystals farther from the surface, are treated with less of the azole compound and, if the rate of diffusion is sufficiently slow, there may be considerably less of the azole compound (even approaching zero) reacting with the lower than with the surface silver halide crystals. In such elements, satisfactory results might be obtained with only a fraction, e.g., one-half, of the amount of the azole compound theoretically calculated as required to just cover the surface of a mole of the silver halide crystals.

With regard to Tests A and B, by reference to the above text or by calculation, it can be determined readily that the organic compound should be present in such an amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin emulsion containing 10 g. of gelatin per mole of Ag and 0.57 mg. of Ag/ml., and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and 100 mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with by weight, aqueous sodium hypochlorite and by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous agitation of the dispersion for 30 seconds at 25 C.

The invention is useful with silver halide layers free from or containing a water-permeable colloid binding agent. In a preferred embodiment of the invention prefogging and azole compound treatment of the silver halide is such that the resulting photosoluble element can not be exposed and developed conventionally to a practical negative silver image due to high fog.

The invention will be further illustrated by but is not intended to be limited to the following examples:

Example I.An aqueous light-sensitive gelatino-silver halide emulsion containing chrome alum as a hardening agent and having a gelatin to silver halide weight ratio of 1:19 (calculated as AgBr) and with a silver halide composition of 70 mole percent chloride and 30 mole percent bromide, was applied at a coating weight of 116 mg./dm. calculated as silver bromide, on a vinylidene chloride copolymer subbed film base prepared as described in Example IV of Alles U.S. Patent 2,779,684. A sample of this coating was treated for sec. with a solution of 0.25 gram of 2-mercapto-4-phenyl-thiazole, hereinafter referred to as MPT, in 458 ml. of solution (solvent consisting of 269 ml. of 95 percent ethanol, ml. acetone, 175 ml. water) and air dried. The dried sam ple was prefogged by a uniform exposure for 5 sec. to a SOD-watt reflector (No. 2) floodlamp (having a maximum beam candle power of 50,000 at 10 feet with a mean color temperature of 3400 K.) placed about 6 inches above the sample, then treated with the MPT solution again for 15 seconds and dried as before. Following this, the sample was sensitometrically exposed through a conventional square-root-of-two step wedge, and a Wratten #16 filter (a yellow filter which transmits less than 1% of light below a wave length of about 510 millimicrons) by a contact printer containing 7 tungsten-filament, 100-watt incandescent bulbs at about 6 inches distance for a total of 4 minutes. The exposed sample was processed for 1 minute in a hardening fixer of pH about 4.7 to 4.8 containing 77 g. of sodium thiosulfate and 10 g. of potassium acetate per liter of solution. The treatment in the fixing solution removed a portion of the exposed silver halide leaving a positive silver halide image in the unexposed areas. This image was washed in water for seconds, then exposed for 5 seconds to the 500-watt reflector photoflood lamp used for the prefogging exposure at a distance of about 6 inches to completely fog the emulsion. The sample was then treated in a high pH developer of the following composition, washed, and dried in the air:

DEVELOPER COMPOSITION H O ml 800 Na SO (anhyd.) g 80 Hydroquinone g 16 1-phenyl-4-methyl-3-pyrazolidone g l Boric acid g 5.5 KBr g 2 NaOH g 24 KI g 2.5

H 0 to make 1 liter.

The positive silver halide image was thus intensified by being reduced to a metallic silver image, demonstrating that an image can be formed by exposure through the yellow Wratten #16 filter.

A control sample was treated as just described above, except that the pre-fogging exposure (and first treatment with MPT solution) were omitted. The control sample showed no positive image visible to the eye (even after intensification) corresponding to the exposure through the Wratten #16 filter. Thus it was seen that a prefogging exposure efiects a definite extension of sensitivity to the longer wavelength portions of the visible spectrum.

Example II.The following compounds were procured:

( 1 Z-mercapto-4-pheny1thiazole (2 2-mercapto-4-cyclohexylthiazole (3 2-mercapto-4 (p-methoxyphenyl thiazole (4) Z-mercapto-4-phenyloxazole (5 2-mercapto-4,S-diphenylimidazole (6) 2-mercapto-4,5-di(p-methoxyphenyl) oxazole (7) Z-mercapto-4-amylthiazole.

A gelatino-silver halide emulsion coating as described in Example I was cut into a number of 6-inch by 35-millimeter strips. Half of the length of each strip was covered by a mask while the other half was white light fogged by a single flash from a high-intensity xenon flash tube strobe lamp Ascorlight operating at its high intensity setting (to give about a ,1 second exposure at a distance of 1 foot).

Seven solutions were prepared, each containing 50 mg. of one of the mercaptans listed above, dissolved in a mixture of 75 ml. ethanol and 25 ml. water. Seven film strips, half-fogged as described above, were each soaked in one of the seven solutions for 30 seconds at 68 F. Each strip was then drained, air dried in an oven at F., and given a square-root-of-two step wedge exposure (across both the fogged and unfogged areas of the strip) for 1 minute using the floodlamp of Example I at volts at a distance of 1 foot.

The exposed strips were processed at 68 F., first for 1 minute in an aqueous solution containing 127 g. of anhydrous sodium thiosulfate per liter to remove the photosolubilized silver halide. After washing in water for 1 minute, the strips were placed for 2 minute in a ph0tographic developer solution (Developer A of Example V), washed 5 minutes in water and air dried at 110 F., all work being carried out under red safelights. Optical trans mission densities of the strips 'were read and below are recorded the densities where there was no imagewise exposure (D and the density at Step #21 where there was maximum exposure, these densities being recorded for both the fogged and the unfogged areas of the film strips.

OPTICAL DENSIIIES Photographic elements made photosoluble by treatment with each of the above seven mercaptan compounds have thus been prefogged, i.e., the silver halide not removed by treatment with sodium thiosulfate was spontaneously developable (under safelight conditions) so as to have much higher D values than found when the prefogging treatment was omitted.

Example IIl.--A gelatin-silver chloride emulsion was digested in the presence of 1.85 grams formaldehyde per mole of silver chloride at 130 F. for 40 minutes, and later digested for 20 minutes at F. in the presence of 0.53 gram of 2-mercapto-4-phenylthiazole per mole of silver chloride. As a final addition, 0.006 mole of KBr per mole of AgCl was added to the emulsion. The emulsion was coated on a vinylidene chloride copolymer subbed polyester base as described in Example I at a coating weight of 66 mg./dm. in terms of AgCl. The dried element was exposed sensitometrically through a Wratten #58 filter (a green filter which transmits less than 1% of light below a wave length of about 480 millimicrons) to a 500-watt reflector type photoflood at a distance of about 6 inches for 4 successive S-second exposures. The exposed element was processed in a sodium thiosulfate hardening fixer of pH about 4.7 to 4.8 for 1 minute, washed for one-half minute, then exposed for 5 seconds to a 500-watt reflector type photoflood lamp as described in Example I at a distance of about 6 inches to completely fog the emulsion. The element was next treated for 1 minute in the high pH photographic developer solution described in Example I, then washed and dried. The resulting sample showed a slight decrease in transmission density in the region exposed to the Wratten #58 filter compared with the density obtained in an adjacent unexposed region.

A control coated element similar to the one just described, except that the emulsion digestion at 130 F. was done without formaldehyde, and the coating weight was 63 mg./dm. in terms of AgCl, was exposed and processed in the same way as the previous element. The control exposure showed no difference in density visible to the eye between the region exposed through the Wratten #58 filter, and an adjacent unexposed region.

This example demonstrates the extension of spectral sensitivity by chemical treatment (pre-fogging) with formaldehyde.

Example IV.A gelatino-silver bromochloride photographic emulsion was precipitated, ripened, washed and redispersed like the emulsion used in Tests A and B. Per mole of silver halide in the emulsion there was added a 1% by weight ethanol solution containing 0.4 g. of MPT (2-mercapto-4-phenylthiazole) and the emulsion was spectrally sensitized with an acetone solution containing 0.025 g. of a merocyanine dye of the structure:

N on, O

The emulsion was stirred for 20 minutes at 160 F., cooled to 95 F., the usual coating adjuvants added, and the emulsion was coated on the film base described in Example I to a coating weight of 50 mg./dm. of silver.

A number of samples of this coating were given an image exposure through a 20-step square-root-of-two photographic step wedge for 10 seconds at a distance of 2 feet from a No. 2 photoflood lamp (as used in Example I) operating at 115 volts. Five of these samples were given uniform preflash exposures (i.e., exposures without a step wedge, prior to the image exposures) with the same light source and distance as for the image exposures but at varying times and voltages as indicated in the table below. A sixth sample received av preflash exposure (a single flash reflected from the ceiling) from a strobe light (Heiland Strobonar 64B strobe flash gun). Three samples received only the image exposure. Two samples received a uniform post flash exposure of 5 seconds at 115 volts at a distance of inches with the same light source as used for the image exposures.

After the preflash and image exposures (but prior to the post flash exposures) all of the film samples were processed for 45 seconds and at 68 F. in the hardening fixer described in Example I and washed in water for 30 seconds. At this point, the last two samples only were given the post flash exposure described above. Then all of the silver halide images remaining were intensified by reduction to metallic silver by treatment for 1 minute in the high photographic developer described in Example I. The samples were washed and dried and the optical 10 densities given in the table below were determined using a densitometer (Western Electric RA-1100-C) with a visual yellow filter.

1 0.5 sec., 50 volts 5 sec.,115 v., 15 in... do

The photographic developer used to intensify the image contained 2.5 g. KI per liter and was able to fog the image sufliciently to partially reduce the silver halide image in the absence of any exposure to light as seen in the data for Sample 7. However, it had been found necessary in practice, prior to this invention, to give a postflash exposure (as the Samples 8 and 9) in order to reduce substantially all of the silver halide to metallic silver. Obviously, much of the silver halide was not reduced in the absence of the postflash exposure (compare the low density of Sample 7 with the much higher densities of Samples 8 and 9).

Samples 1 through 6 (preflash but no postflash exposure) have good optical densities after intensification. With optimum amount of preflashing, the optical densities generally will be found to be no more than 1 to 5% below those found when postflashing is used. Preflashing has an actual sensitiometric advantage in that the sensitivity to light is increased by about 20 to 40% over the sensitivity when using the postflashing technique. A more important practical advantage, however, resides in the fact that the image-exposed film can be processed completely under darkroom conditions with the absence of any annoying flashing procedures which could interfere with other processing operations going on in the same room. For a commercial product, the photographic film element would logically be fogged, according to the teachings of this invention, at the time of manufacture. Thus the processor can avoid the extra, and sometimes very undesirable, step of postflashing.

Example V.This example further demonstrates the nature of the film elements of this invention which are pre-fogged so as to have spontaneously developable" silver halide crystals. A practical limit for the pre-fogging is that a minimum of 25% by weight of the crystals must be developable (i.e., reduced to metallic silver) in the absence of other treatment by radiation or chemicals when given a Fix and Wash (as defined below) and then developed for 3 minutes at 68 F. with conventional agitation in a specified photographic developer solution, i.e., a solution of the following composition:

DEVELOPER A G. p-Methylaminophenol hydrogen sulfate 3.0 Hydroquinone 9.0 Na SO anhyd. 50.0 K CO 50.0 KBr 4.5 KI 2.0

Water up to 1 liter.

and given a Final Fix as defined below.

To demonstrate further the nature of the invention, another developer was used under the same conditions of time, temperature and agitation. This developer, designated as Developer B, was identical to Developer A except for omission of potassium iodide. Developer A is capable of developing both surface and internal latent 11 12 images while Developer B is primarily effective in decontaining Developer A, which is the sequence of normal veloping surface latent images. photosolubilization processing (fixing to form a positive Two types of pre-fogging exposures were used: image and then intensifying), it is seen that in the absence Type I (to form primarily a surface latent image) of prefogging there is virtually no developed silver While was a low intensity light fogging with a No. 2 reflector 5 Type I and Type II prefogging treatments give, respecphotoflood lamp at a distance of 2 feet for 5 seconds at tively, 17.1 and 17.2 mg./dm. silver contents. Since the 30 volts. unprocessed coatings had silver contents of 61.6 mg./dn1. Type II (to form both surface and internal latent these values mean that 27.7% and 27.9%, respectively, of images) was a high intensity light fogging consisting of 1 the total weight of the silver halide was spontaneously flash from an electronic flash tube (Heiland Stronobar" developable. 64B) placed on the test table next to test sample with The requirement that these values exceed 25% prolight directed to reflect from a white ceiling 65 inches vides practical limits for the required extent of the preabove the table top. fogging treatment. With insuflicient pre-fogging, less than Flash designates an exposure applied later (after image 25 of the silver halide can be reduced to metallic silver. solubilization) using a N0. 2 reflector photoflood at Also, it is obvious that excess pre-fogging by light will 15 inches for 5 seconds at 120 volts. photosolubilize the silver halide causing loss via solubi- Fix and wash designates a 1-minute treatment at lization during the Fix & Wash part of Sequence 0 to 68 F. in an aqueous solution of sodium thiosulfate, 10% the extent that less than 25 of the silver halide remains by weight, followed by a half-minute wash in Water at for conversion to metallic silver. 68 F. Whereas Sequence 0 represents the normal photosolubi- Final fix designates a 5-minute treatment at 68 F. in lization processing of areas of an element receiving no the hardening acid fixer of Example I followed by a 10 imagewise exposure, Sequence a represents the correminute water wash at 68 F. and drying of the sample sponding process in areas receiving full imagewise expoin air. This final fix while not used in the regular imagesure. Less than 1% of the silver halide has been develforming photosolubilization process, adds to an underoped to metallic silver in such fully exposed areas since standing of the process by removing any final, residual the first step of the processing sequence (fixing) has resilver halide which is not reduced to metallic silver by moved the photosolubilized silver halide before it could one of the developer solutions. Thus the readings of be developed. Therefore, Sequences aandctaken together silver in mg./dm. at the end of processing, which are demonstrate that the pre-fogged photosolubilizable film obtained by X-ray fluorescence, will show only developed element is capable of giving a positive silver halide image which can be intensified in a photographic developer withsilver.

A number of film samples were taken from a coating out immediate prior flashing with light. like that described in Example IV except that the coat- The prefogglng exposure and other conditions are not ing weight was 104 mg./drn. of silver halide, calculated fully opt1m1zed 1n this example as can be seen by comparas AgBr. These samples were given a light-fogging exmg Sequences b and 0. Although Sequence a shows that posure of Type I or Type II and then processed accordover 25% of the silver hal1de 1s spontaneously developing to one of the sequences a, b, c, d or e as indicated able, the eXtra flash ng step of Sequence b (prior to the in the table below. The optical transmission densities (D) development p) fl? the Potal developed sllvel" P of the processed strips were determined as in Example to about 35% of that or1g1nally 1n the element. IV. The silver content, Ag, was determined in units of Sequences and e, taken together, show that the elemg./dm. by means of X-ray fluorescence. Several samples ment, with either Type I or Type II prefogging, is not of the coating were found, in the absence of any processsuitable for conventional processing (wherein developing, to have an average silver content, Ag, of 61.6 ment precedes fixing) to give a negative image. It is obmg./dm. vious that there is insufficient difference in the amount of Processing sequence a b c d 0 Flash F'n &Wash xxxx xxxx xxxx Fix & Wash Flash Fix & Wash Flash :1 x x x Developer A Final Fix Light fogging D Ag D Ag D Ag D Ag D Ag None .03 0.4 3.10 21.8 0.00 0.2 3.68 28.3 0.00 0.4 Type .05 0.4 3.18 21.3 2.20 17.1 4. 0+ 32.5 2.22 17.6 Type II .03 0.3 3.20 22.0 2.20 17.2 3.80 28.3 1.66 14.6

The above processing was carried out on other samples developed silver and in the optical transmission densities of the coating except that Developer A was replaced with between areas receiving full imaging exposure (Se- Processing sequence a b c d a Flash Fix&Wash xxxx xxxx xxxx Fix & Wash Flash Fix & Wash Flash x x x x Developer B (which contained no KI) The following information obtained from the table is quence d) and areas receiving no imaging exposure (Seof significance to this invention. 7 O quence e). Thus the densities recorded in Sequence e rep- First, the photosolubilizable elements of this invention resent undesirably high fog densities. require pre-fogging to the extent that at least 25% by The second set of processing data involving the use of weight of the silver halide crystals must be spontaneously Developer B (without potassium iodide) are included for developable by the prescribed treatment in Developer A. the sake of completeness but merit less discussion. With Referring to processing Sequence 0 with potassium iodideprefogging by means of light, there is sufllcieut internal 13 fogging of the crystals that it is definitely preferred to employ a developer such as Developer A which is capable of reducing both surface and internally fogged crystals.

Example Vl.--Chemical pre-fogging has been found to be more efficient than prefogging by light and, among the chemical agents used, formaldehyde or formaldehydeyielding compounds are particularly preferred. One mole of a gelatin-silver chloride emulsion, containing 105 g. of gelatin, was digested for 40 minutes at 130 F. in the presence of 1.87 g. of formaldehyde. Later it was further digested 20 minutes at 170 F. in the presence of 0.76 g. of 2 mercapto 4 phenylthiazole and 0.025 g. of the optical sensitizing dye of Example IV. The emulsion was coated on the film base of Example I at a coating weight of 58 mg./dm. of silver chloride. A control coating was prepared in a similar manner but no formaldehyde was present to efiect pre-fogging.

Samples from the two coatings were processed according to the 5 processing sequences described in Example V, using Developer B (containing no potassium iodide) for intensification.

The results are shown below:

OPTICAL TRANSMISSION DENSITIES Processing sequence Flash Fix and Wash xxxx Fix and Wash Flash Fix and Wash Developer A Final Fix Processing sequence while there is almost no spontaneous development in the non-prefogged coating.

Very similar results are obtainable when Developer A (containing potassium iodide) is substituted for Developer B.

Example VII.-Chemical prefogging was effected by stannous chloride as follows: One mole of a gelatin-silver chloride emulsion, containing 101 g. of gelatin, was digested for 40 minutes at 130 F. in the presence of 0.07 g. of SnCl '2H O. Later it was further digested 20 minutes at 170 F. in the presence of 0.75 g. of 2-mercapto-4- phenylthiazole and 0.025 g. of the optical sensitizing dye of Example IV. The emulsion was coated on the film base of Example I at a coating weight of 52 mg./dm. of silver chloride. A control was prepared in a similar manner but no stannous chloride was present to effect prefogging.

Samples from the two coatings were processed according to processing Sequences a, b and 0 described in Example V, but using the following developer formulation for intensification.

Water ml 800 Na SO (anhyd.) g 80 Hydroquinone g 16 1-phenyl-4-methyl-3-pyrazolidone g 1 7 Boric acid g 5.5 NaOH g 16 0 5 M KI ml 30 Water to make 1 liter.

pH at 68 F. 12.5

reaction than the selective reduction required in conventional photographic processing where it is necessary to reduce only that silver halide which has been exposed to light.

Example VIII.-A photographic layer Was made by evaporating silver chloride onto the film base described in Example I, using a High Vacuum Evaporator, Model No. SC 3 (Optical Film Engineering Co.). The vacuum apparatus employed a tantalum ribbon and operated at a pressure of 3 10- microns of mercury. Using about 280 milligrams of AgCl at a distance of 24 cm. from the film base, a coating weight of Ag'Cl of about 4 mg./dm. was obtained.

The vacuum-coated film was bathed for 15 sec. in the ethanol-water (25/10) solution of 2-mercato-4-phenylthiazole of Example I, dried and exposed stepwise for 5, 10, 20, 40 and seconds to a photofiood lamp (General Electric 2A) at a distance of 6 inches. The exposed element was then immersed in 12.8% aqueous sodium thiosulfate for 30 seconds, rinsed in water for 10 seconds and then bathed in a developer solution as described in Example I. All operations were carired out under illumination from white fluorescent lamps. Such illumination during the preparation of the element and subsequent steps provided the pre-fogging required according to this invention.

A direct-positive image was formed by the 5, 10, 20 and 40-second exposure, i.e., imagewise density decreased with increasing exposure. However, when the exposure was increased to 80 seconds, a negative image was formed, the system reversing or solarizing by increased exposure like conventional silver halide systems.

An important advantage of the novel elements of this invention over those of the listed applications is their enhanced spectral sensitivity. These elements can be exposed by light of various wavelength and can, therefore, produce more faithful recordings of original scenes. A very practical advantage is shown in connection with Example IV wherein it is demonstrated that prefogging (which could be carried out during manufacture of the film) could eliminate post-flashing and any disadvantages thereof.

The most obvious advantage of the novel elements of this invention is the extension of their spectral sensitivity. These elements can be exposed by light of various colors and can, therefore, produce more faithful recordings of original scenes.

Another advantage of this invention is that it provides new elements for forming silver images that do not require special equipment but instead can be used with conventional equipment and apparatus. A further advantags is that the elements can be used successfully by photographers of ordinary skill. A still further advantage is that the elements can be processed with conventional reducing agents, e.g., developers and conventional fixing agents. Yet another advantage is that the new elements can be used to produce images without selective reduction.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A photosoluble silver halide dispersion comprising, before imagewise expo-sure to radiation, light-sensitive silver halide crystals having associated therewith in substantially greater than fog-inhibiting amounts a silver salt of an organic compound of the formula where X is a member selected from the group consisting of S, O and NH, R is a hydrocarbon nucleus of 4-8 carbon atoms, and R is hydrogen or a hydrocarbon nucleus of 48 carbon atoms, said salt being of lower solubility in water than silver chloride; the silver halide crystals so associated with the silver salt being less soluble in aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH and the associated silver salt being present in such an amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin emulsion containing 10 g. of gelatin per mole Ag and 0.57 mg. of Ag per ml., and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and 100 mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous and essentially equal agitation of both dispersions for 30 seconds at 25 C.; characterized in that the silver halide crystals are spontaneously developable to the extent that over 25% by Weight of the silver of said crystals remains as reduced silver after dissolving, washing and development for 3 minutes at 68 F. in an aqueous developer of the following composition:

G. p-N-methylaminophenol hydrogen sulfate 3.0 Hydroquinone 9.0 Na SO 50.0 K CO 50.0 KBr 4.5

KI -a 2.0

Water to make 1 liter.

treatment for one minute at 68 F. in a 10% aqueous solution of sodium thiosulfate, washing for one half minute with water at 68 F., treatment for 5 minutes at 68 F. in a hardening aqueous fixing solution of pH about 4.7 containing 77 g. of sodium thiosulfate and 10 g. of potassium acetate per liter of solution followed by washing in water at 68 F.

2. A dispersion according to claim 1 wherein said silver salt is a mercaptide of Z-mercapto-4-phenylthiazole.

3. A dispersion according to claim 1 wherein said silver salt is a mercaptide of Z-mercapto-4-cyclohexylthiazolc.

4. A dispersion according to claim 1 wherein any heavy metal salt present is a noble metal salt.

5. A dispersion according to claim 1 wherein there is present a water-permeable organic colloid binding agent for the silver halide crystals.

6. A photographic element comprising a support comprising a layer of a photosolubilizable silver halide dispersion comprising, before imagewise exposure to radiation, light-sensitive silver halide crystals as defined in claim 1.

7. An element according to claim 1 wherein said silver salt is a mercaptide of Z-mercapto-4-phenylthiazole.

8. An element according to claim 1 wherein said silver salt is a mercaptide of 2-mercapto-4-cyclohexylthiazole.

9. An element according to claim 1 wherein any heavy metal salt present is a noble metal salt.

10. An element according to claim 1 wherein there is present a water-permeable organic colloid binding agent for the silver halide crystals.

11. An element according to claim 1 wherein the layer 'is free from a binding agent for the silver halide crystals.

12. A process which comprises giving an overall prefogging exposure to a light-sensitive silver halide layer and then admixing therewith in substantially greater than fog-inhibiting amounts a silver salt of an azole compound of the formula:

where X is a member selected from the group consisting of S, O and NH, R is a hydrocarbon nucleus of 48 carbon atoms, R is hydrogen or a hydrocarbon radical of 48 carbon atoms, said salt being of lower solubility in water than silver chloride; the silver halide crystals so associated with the silver salt being less soluble in 10% aqueous sodium thiosulfate than untreated silver halide crystals at a predetermined pH and the associated salt of the azole compound being present in such an amount, in terms of the ratio of its weight to the surface area of said silver halide crystals, that when admixed in such ratio with an aqueous silver chlorobromide (70/30 mole percent) gelatin emulsion containing 10 g. of gelatin per mole Ag and .57 mg. of Ag per ml., and said silver chlorobromide dispersion is treated with 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver and mg. of sodium thiosulfate), at least three times the amount of silver chlorobromide remains undissolved as compared with a similar dispersion successively treated with 5%, by weight, aqueous sodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (so that the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg. of sodium thiosulfate), after vigorous and essentially equal agitation of both dispersions for 30 seconds at 25 C.

13. A process according to claim 12 wherein said fogging exposure is a chemical fogging exposure.

(References on following page) 1 7 References Cited UNITED STATES PATENTS OTHER REFERENCES Sheppard, S. S.: The Optical Sensitizing of Silver Halides by Colloidal Silver, in Franklin Institute Journal, pp.

587-590, November 1930.

NORMAN G. TORCHIN, Primary Examiner R. E. FICHT ER, Assistant Examiner US. Cl. X.R. 

